Where in Norway did you visit? The further south you get thus more polite, outgoing etc you get. Of course people are different and how you behave vary, but there are loads of people who are very honest and direct.
What is not the norwegian way is to be fake-modest. If you don't believe you will win you of-course not say that, but if you believe you will win, like Jakob, you say that. Telling lies is worse. You are right that being shy/reserved/quiet are also typically traits, but I think what is mostly overlooked when it comes to Jakob is that he doesn't seek out reporters but answers the questions he get. He is not arrogant/showboating compared to the champs in the lower distances, but somehow get more hate. But sure, he and his family is not by any means typical for the standard norwegians. When it comes to showboating check out Petter Northug, legendary skier, https://youtu.be/N1uFssbp7nE?t=38 . Brutally honest but also a showboater to boot. (2 olympic gold, olympic silver and bronze, 13 WC golds). Equally hated and loved by the Swedes, Finns and Russians.
Sorry for this rambling, I kind of wrote as I though about the subject.